This one exists, as far as anyone can tell, only from the air. A roughly oval enclosure near Rockspring in north County Cork, measuring around forty metres across, has never been excavated or formally surveyed on the ground. What we know of it comes from a single aerial photograph taken in July 1989, in which the outline of a fosse, the ditch that would once have defined the boundary of the enclosure, shows up as a cropmark. Cropmarks form when buried features affect how crops or grass grow above them: a filled-in ditch retains more moisture than the surrounding soil, producing a slightly lusher, darker line of vegetation that becomes visible from altitude under the right conditions of drought and low sun.

The shape itself is quietly informative. The northern and southern sides curve broadly, while the eastern and western sides are slightly flattened, giving the whole outline a softened rectangular quality rather than a true circle. The corners are rounded. This combination, oval rather than circular, slightly angular at the sides, is consistent with the kind of enclosed farmsteads or ringfort-related features found across early medieval Ireland, though without excavation no date can be assigned with confidence. The fosse would originally have been dug to throw up an earthen bank on the interior, creating a defended or bounded space for a household, its animals, or both. Thousands of such enclosures survive across the Irish countryside in varying states of preservation; this one has been reduced entirely to a shadow in the soil.